Spring device



Aug. 4, 1953 w. J. cooK 2,647,743

SPRING DEVICE Filed June 29. 1949 4 Sheets-Sheet 1 Force Defleciion FIG. 2.

FIG. 3.

I INVENTOR. W/LL/AM J. COOK BY 3 1 q ATTORNEYS.

FIG. 4.

Aug. 4, 1953 w. J. cooK 2,647,743

SPRING DEVICE Filed June 29. 1949 4 Sheets-Sheet 2 INVENTOR. W/LL /AM J, COOK ATTORNEYS.

Aug. 4, 1953 w. J. COOK 2,647,743 SPRING DEVICE Filed June 29, 1949 4 Sheets-Sheet 3 m W/lYL MM J.

ATTORNE YS.

FIG: /2

g 4, 1953 w. J. COOK 2,647,743

' I SPRING DEVICE! Filed June 29. 1949 4 Sheets-Sheet 4 INVENTOR. WILL IAM I COO/f ATTORNEYS. I

Patented Aug. 4, I953 SPRING DEVICE William I. look, Lansdale, Pa., assignor, by mesne assignments to Eastern FFl-C.

Metals Research I Q blew York, N. Y., a corporation of New rk Application June 29, 1949, Serial No. 102,117

(01. zeal-1) 4 C aim This n en i n el es to a some de ice,

he onvent ona p i ices he e o o used have a common characteristic. namely. a posit v rad en hat is. the gr ater the defle ti n o the sprin the re ter isthe otal o e exert d by the s r n rl has lon bee s u h 9 develo a sp n device aving a ero radi n or a negative gradient. Further, it has long been qes ed and nev r achieved to have a sp ce whi h has a va iable ra i nt. f r exampl including a plu al ty .of positiv ne ative and zero radients. Again the pr l m o making a spr n having an initial orce at initial defl ction which is high compared to the maximum force which the pring can exert has not be n overcome heretof ore.

Previously known springs have been limited in usefulness due to their restricted range of action which, for example, is normally about two times its original length spring. The working ran e ofsuch .a sprin in many cases is desirably thirty to fifty times its original dimension.

Applicant has solved these and other problems by providing a coil spring device in which the force exerted by the spring is determined only by the. force necessaryto overcome the set of that portion of the spring which is being unwrapped.

It is, therefore, an object of this invention to provide a spring device which will exert a constant force at all times irrespective of the amount of deflection.

A further object of this invention is to provide 'a springdevice which has a negative gradient,

that is, which will, for each additional increment of deflection, exert a smaller total force.

A still further object of this invention is to provide a spring device which has a plurality of gradients varying from positive to negative.

An additional object of this invention is to provide a spring device which will exert an initial force at an initial deflection which may be as high as the maximum force which the spring device can exert.

An additional object of this invention is to provide a spring device which has a large range of action greatly exceeding its original dimensions.

An additional object of this invention is to provide a spring device which will act around corners without losses or inaccuracies with cableslike freedom.

An additional object of this invention is to provide a springdevice which has a far greater capacity than a conventional coil spring made from the same amount of material tostore energy.

in the case of an extension -ments of the extended Th se and other j ts o this invention wil be ome app r nt from th follo n des ript on.

read in conjunction with the accompa ng-drawadapted to produce a spring in accordance with t s-i venti n;

Figure 4 is a section taken 0 he plane indisate by the l ne 4-4 ,iIiFi llre :3;

Figure 5 is a schematic view of a spring device in accordan e wit t is i on sho ng s smcnts of the extended portion of the spring severcd from the spring and permitted to assume their natural shape; r

Figure 6 is a sch matic view of a sprin devi n cc dance wi h th s nvention show n sesments of the ex nde or ion of the spring sew cred from the spring and permitted. to assume their natural shape;

Figure '7 is a schematic view of a spring device in accordance with this invention showing segportion of the spring severed from the spring and permitted to assume their natural shape;

Figure 8 is a schematic showing or a spring device in accordance with this invention illustrating a spring designed to exert a constant force at all deflections;

Figure 9 is a schematic showing of a spring device in accordance with this invention illustrating a spring designed to exert a decreasing'force as it is extended;

Figure 10 is a schematic showing of a spring device in accordance with this invention illustrating a spring designed to have a gradient varying from negative to positive;

Figure 11 is a schematic showing of a spring device in accordance with this invention utilized to exert a torque on a bushing freely mounted on s a Figure 12 is a section taken on the plane indit d y the l ne Il -42 of Figure l1;

i mtioo h an el ipt al spool mounted for rofictio Figure 15 is a schematic showing of a convenby line A in Figure 1.

stantially repeats this cycle.

tional loose coil spring showing one end secured to a shaft;

Figure 16 is a showing of a portion of a stapler as illustrative of the utility of a spring device made in accordance with this invention and capable of exerting a constant force at al1 deflections;

Figure 17 is a front elevation view ofa spring device in accordance with this invention adapted for use as a clamp;

Figure 18 is a schematic representation of the manner in which a spring in accordance with this invention is adapted to, in effect, go around corners;

Figure 19 is a schematic showing of spring in accordance with this invention;

Figure 20 is a plan view of a clip in accordance with this invention; and

Figure 21 is a plan view of a clip having overlapping ends in accordance with this invention.

A conventional compression spring has a substantially constant positive gradient K as shown As shown in Figure 1, for a positive increment of force AP, the spring will be deflected a positive increment of length AL. Since gradient AP AL it will be apparent that the gradient is substantially constant in the working range and always positive. The characteristics of a typical extension spring are shown by line B in Figure 1. It will be apparent from a comparison of line B with line A and a consideration of the above discussion that gradient Kof the extension spring throughout its working range is substantially constant and always positive. The springs whose characteristics are shown by the lines A and B are typical of springs heretofore used.

The spring in accordance with this invention can be formed to exhibit characteristics very different from those of the above discussed conventional spring device. Thus, for example, a spring device in accordance with this invention may exhibit the characteristics indicated by line C in Figure 1, that is, such a'device may have a zero gradient or, expressed another way, such' a device exerts a constant force irrespective of the length of deflection. Such a spring, it will be apparent, has a multitude of applications.

Again a spring device in accordance with this invention may have a negative gradient K as illustrated by the line D in Figure 1. Here, for a positive increment of length AL, the force decreases by a negative increment of force in AP, '5

since may be formed with positive, negative and zero gradients. Thus, observing line E, it will be seen that it starts out with a decreasing positive gradient which goes to zero and. then becomes negative, gradually becomes more positive, reaches zero, becomes increasingly positive and then 'sub- The manner in which these gradients are achieved will be made apparent in the following description.

a helical Now, as illustrated by the line E in Figure 1, a spring in accordance with this invention A sprin 2 in accordance with this invention is shown in Figure 2, The spring 2 has a plurality of wraps 4. The spring 2 may be formed from strips of any resilient or springy metal commonly used in forming springs, thus, for example,

stainless steel or a high carbon spring steel may be used. 11-; is preferable "to utilize 'iiat, strips of such material in forming the spring" although various cross sectional shapes may be used.

It will be noted that each wrap 4 is in contact with its adjacent wrap 4. In the formation of the spring 2, it is necessary to put a set or stress inthe strip 6 used toform the spring. As shown schematically in Figure 3 the set may be introduced by passing strip 6 through a setting device 8 which comprises rollers 10 and I2. A bracket I4 is secured to shaft 16 of roller 12 and shaft l8 of roller I0. Bracket I4 permits roller In to be moved in relation to roller l2 so as to vary the amount of set introduced into strip 6. It will be apparent, of course, that the set may be also varied by numerous other means such as, for example, by changing the size of roller l2.

' As shown in Figure 3, after ase't is introduced into strip- 6, the strip passes through a guide 20, a pair of feed-rollers '22 and 24, a guide 26, which is identical "to guide 20 and is coiled as shown spring is in use. This requirement places certain limitations on the amount of set put into the strip forming the spring. Thus, where the spring is free to rotate on'its natural axis, the

set must .begreatenough so that the strip will naturally form a tight solid coil in order that an extension of the spring will not result in a change of the inner radius of the spring or of any of the coiled wraps. It will be apparent that this limitation will depend largely on the resiliency characteristic of the metal .used and the frictionbetween the wraps. Where'the spring is to be coiled onto a core such-as, for example, a bushing mounted for rotationon a. shaft,-the limitations as to set are less restricted. In such a case, the spring need only be formed with such setso that each wrap oreach incrementof a wrap will naturally attempt to assume the shape of a portion of a circle which has a smaller radius than the'surface on which it is to lie. Thus, each increment of the innermost wrapwould, of necessity, have a natural radius equal to or smaller than the radius of the core onwhichit was coiled. Again, by wayof example, each increment of the fourth wrap would have a radius equal to or smaller than the radius of theincrement of, the third wrap against which it was coiled.

The reasons .for .the above requirements are made obvious when the principle under which the invention operates is understood. The force of 9. spring device in accordance with this invention results when the spring is uncoiled. It is the section of the spring which is in the process of being straightened out by being drawn off the tight coil but which hasnot yet been fully straightened which exerts the-force. The portion of the spring remainingin the solid coil and the portion which hasbeen straightened out exert that if the spring is straightened 5 no force. Thus it will be apparent that as the spring is extended or contracted constantly changing sequential segments of the spring act to exert the spring force. By varying the preset in these segments, it 'will'be noted that the force exerted will be varied or if the preset in the segments is constant then the force exerted will be substantially constant,

For satisfactory operation, it will be observed that there should be no slippage between the wraps and that the wraps should betightly coiled otherwise forces other than that created incident to unwrapping will'be introduced.

The force exerted by the segmentof spring in V accordance with this invention being unwrapped and therefore the total force being exerted by the spring is shown by the following formula where the spring is mounted, for example, on a spool:

E1 1 l 1 ift a 5:1

where F= the force exerted at the free end of. the spring;

E=modulus of elasticity;

I =.moment of inertia of. segment uncoiling which This formula is subject. to a very slight inaccuracy due. to the energy lost incident to the formation of a lateral camber in the uneoiling segment such as is shown in Figures 4 and 12.

Observing the above formula, it, will be.- seen out, R1 will be infinite and the formula will read Since the expression within the bracket reduces to zero, F will be zero. This. proves that when a segment of the spring has been straightened out it no longer exerts any force- It. is believed that the underlying theoryand the operation of'this invention will be clarif ed by reference to Figures 5, 6 and In. Figure 5, a

sprin 32, which: w s m de t e ome ay t a ,Spring 32 was formed by setting or stressing a flat metal strip so that each. increment 42- of. the strip would tend tov naturally assume a position on a circle of a radius smaller. than the radius of bushing 34, The. increments 42 are shown schematically as severed. from the. extended. portion of thev spring. Each increment 42 has assumed its natural. ra.- dius, the radii of the segments all being equal. in this case. It. will. be clear that the force exerted by spring 32 as it is extended will be equal to the force being exerted to unwrap the 111C118.- ments 42 which lie betweenthe last increment which is supported by the coiled. wraps and the portion of. the spring which is straightened. out,

arrows at 44. Since all of the increments 42 t s rt n Qi-th sp in b n indi ted by have been given the same-set, it will beapparent that, irrespective ofthe'amount which spring 32 is extended, it will. exert the same force.*- Thus spring 32 exhibits trecharacteristics indicated by line C in Figure 1, that is, it has a zero grasdient.' i Referring now to Figure 6, a. spring 46'='which was made the same wayspring. 2 was. forinedis mounted on a bushings which is adapted to 1'0! tate freely on' shaft'5fl. End 52' of spring Mifihas been extended by a force exerted in the direction indicated by arrow 54'. Spring 46 was: formed'by setting or stressing a fiat metal strip so thateach increment 56 of the strip would tend'to naturally assume a position on a; circle. The set put in the fiat metalstripwas gradually decreased from-the inner end of the spring to the outer end. The increments 56 are shown schematically as severed from the extended portion of the. spring, each'incrementhaving assumed its natural radius. It will be noted'that the natural'radiiydeicrease as we progress from the coiled portion: of the spring to the end 52. Here again, as in' the case of spring'32, the force exerted by springv 46 results from the unwrapping of increments 56 in the'area indicated by the arrows at 58; that is, in the area between the coil portion and :the straightened out portion of the spring 46. As the spring is extended, the natural radii of'the segments- 5B in the unwrapping area gradually=del creases. Thus the force necessary tounwrap the successive groups of increments lying in the unwrapping area gradually increases which, in turn, of course, means that the total force'exertedby the spring gradually" increases thus giving" the spring a positive gradientf Depending upon the rate of change of the natural radii'of thei increaments: 56'; the positive gradient of spring. dfimay be constant or varying. r

Referring now to Figure '7, a'spring Sll'formed 'ass'pring 2' was formedis mounted on a bushing 62 which is adapted to rotate freely on shaft. End GG-of spring'GG has been extended by force exerted in'the direction indicated by arrow 68.. Spring 60 was formed by setting a flat metal strip to provide increments 10 having gradually'decreasing natural radii from the inner end of springt fl to the end 66-.

The increments 10 are shown schematicallywas severed fromthe-extended' portion of thespring, each increment 10 having-assumed its natural radius. Here; again, the force exerted by the spring is the force being exerted to unwrap the segments- 1!! which lie in theunwrapping' area (see arrows at T2) which-is the area lying between the coil portion ofthe spring 60 and that portion which has been straightened out. As end- 66' is extended, the natural radii of the segments 10 lying in the unwrapping area gradually increases andthus' the total force exerted by the spring as it is extended decreases; Thus spring 60 has the characteristics indicated by line D in Figured, that is, it has-a'negative gradient; Referring now to Figure 8, we have by way' of i'urther specif c examples a spring 14 made like spring 2 and mounted on a bushing H5 which is adapted to rotate freely on shaft ill. The inner end 19 or" the spring l l is bent over to engage a slit in bushing 76. Spring 74 was formed bysetting, a hat metal strip of stainlesssteel so that 'pur nesesp illustratmg the fae ha sueh'a sp ii has a substantially zero gradient, a we'i ht'w] is schematically shown secured to the outer end of spring I4 in two different positions. This :clearly illustrates that for any given pointof extension of spring 14 the force exertedv by the spring will be substantially constant and counteracted by a fixed weight WI, it being appreciated thatthe total force exerted by the spring is the force being exerted to unwrap the spring in the area indicated by the arrows at 8|.

Where it is desired that spring I4 very accurately exert a constant force through its operating range, this may be accomplished by varying the set in the spring. It will be apparent that, since the outermost wraps are attempting to conform to surfaces having greater radii than the innermost wraps, the force exerted by the spring when the outermost wraps are being uncoiled will. be slightly less than the forces successively exerted by uncoiling the innermost wraps. To overcome this variation in the exerted force, it is only necessary when forming the spring to gradually increase the set in the spring from the innermost wrap to the outermost wrap. Thus the increased set in the outermost wrap will compensate for the fact that this wrap is conforming to a greater radius than the innermost wrap and similarly all of the other wraps will be compensated for the varying radii on which they are coiled and thus the spring 14 can accurately exert a constant force-irrespective of extension and has the characteristics shown by line C in Figure 1.

As shown in Figure 9, a bushing 80 is freely mounted for rotation on a shaft 82 and has coiled thereon a spring 84. Spring 84 was formed with a set which gradually increases from the inner the set of the innerthat the increment wrap to the outermost wrap, most increment being such would naturally assume a radius smaller than the radius of the bushing and every segment has a natural radius which will cause it to lie tightly-on the surface beneath it. The force exerted by the spring is that being exerted to unwrap the increments in the unwrapping area indicated by the arrows at 86. Thus, as shown in Figure 9', when the spring 84 is extended to a position where weight WI is secured to it, it will exert a fairly considerable force. Again, as shown, if weight WI is removed and the spring extended to the position shown in support of weight W2, it will exert a smaller total force as indicated by the fact that weight W2 is smaller than weight WI. Again if we discard weight W2 and extend the spring to the position shown in support of weight W3, it will be apparent that spring 84 will exert a force smaller than that represented by weights WI or W2. Such a spring has the characteristics shown by line D in Figure 1.

In Figure 10 is shown a bushing 88- freely ,mounted for rotation on a shaft 90 and carrying a spring 92 in accordance with this invention. Spring 92 is set so as to have various gradients both positive and negative. The portion of the spring which is first uncoiled has a negative gradient, subsequent portions uncoiled having a positive gradient. This, of course, is achievedby having in the portion first uncoiled a progressively decreasing amount of set while the positive gradient in succeeding coils of the spring is achieved by progressively increasing the set. The set of each increment must, of course, insure that the increment has a natural radius which causes it to hug the surface below it. These characteristics of spring 92 are illustrated by the schematic showing of weights W4, W5 and W6 which, as indicated, will balance the force exerted by spring 92 at various points ofextension of the spring, it being understood that the total force exerted by the spring is that force being exerted to unwrap theincrements lying in the upwrapping area indicated by the arrows at 94. Thus as'the spring is extended from thepoint where it will balance weight W4 to the point where it will balance weight W5 the gradient is decreasing as evidenced by the fact that weight W5 is smaller than weight W4. As the spring is extended from the point where it will support weight W5 to the point where it will support weight W6, the gradient of the spring is increasing rapidly as evidenced by the fact that weight W6 is markedly greater than the weight W5 or even weight W4. Such a spring has the characteristics represented by the center part of curve E in Figure 1. v

Figure 11 shows a spring in accordance with this invention utilized to introduce a fixed resistance to the motion of a shaft. Here a bushing 96 is freely mounted for rotation on a shaft 98 and carries a spring I00. Spring I00 is formed with a slightly and progressively increasing set from the interior wrap on bushing 96 to the exterior wrap so, as in the case of the example of Figure 8, it will exert a constant force irrespective of the amount of extension. The set of the interior wrap is such that it will have a natural radius of curvature equal to the radius of the bushing 96. A portion of spring I00 is extended to a bushing I02 and coiled thereon. Bushing I02 is keyed to shaft I04. It will be apparent that the uncoiled and unstraightened portions of spring I00 adjacent bushings 96 and I02 in the upwrapping areas indicated by arrows at I06 and I08, respectively, will result in a net force tending to rotate bushing I02 counterclockwise since the portion of the spring adjacent bushing I02 is more opened out against the set than is the portion adjacent bushing 96 due to the fact that it is coiled on a greater radius. It will further be apparent that this net force will remain substantially constant irrespective of the number of turns clockwise or counterclockwise of shaft I04. 6

As shown in Figure 14, the force characteristics of a spring in accordance with this invention may be varied by the shape of the core on which thespring is mounted. Here a spring I 08 in accordance with this invention is mounted on an elliptically shaped mandrel I I0 which has its center mounted for rotation on a shaft II2. A constant set has been placed in the spring I09 such that the natural radius of each increment of the spring is smaller than the minimum radius of the surface of the core.

As we have seen before, if such a spring were mounted on a round mandrel or bushing, the force exerted by the spring would be constant irrespective of the amount of extension of the spring. Here, however, the elliptical shape of the core IIO modifies the force characteristics of spring I08 in such a manner that the force characteristic curve of the spring becomes sinusoidal, that is, the gradient of the spring will awa e will be apparent that the more the mounting surface prevents the spring increments from assuming their natural radii, the ,less will-be the; force necessary to straighten out these increments. Thus, as here, by varying. the shape of the mounting surface the force which agiven increment of a spring in, accordance with this invention can exert can be varied. r Referring, now to Figure. 15, a strong contrast with the springs in accordance with this irivention is provided by a conventional spiral spring H8. Spring I18 has its inner end fixedly secured to a shaft I20 and a free outer end I22. By way of contrast with the spring in accordance with this invention, it will be no'tedthat the coils of Spring 1 I8 a're'riot in contact with each other. If a force is exerted in the direction indicated by arrow I23, the entire f length (if s ring H8 actSlike a long can beam to exert a torque on shaft I20. This is in strong "contrast with the'above discussed springs'made in accordance with this invention and which are adapted toexert their total force through the medium of that portion of the springwhich is being straightened out, that. is, the portion of'the spring lyingin the unwrapping zone between .the coil and the straightened out portion or the spring. It will be apparent that no constant or negative gradient could be achieved with spring H8 as is demonstrably achievable with springs in accordance withthis invention.

The schematicallyshown staple feeder I26 (see Fig. 16) further exemplary 'of the use ofa spring in accordance with this invention. Here the staplefeed slide I28 travels on rail. I30. A

constant force spring I32 having a fixed set resulting in a natural radius of curvature equal to the radius of bushing I34 is coiled on bushing I34 which is freely mounted for rotation on a shaft I36 and the free end of-the spring extends to slide I28 ancl'is' secured thereto by a shoe I38.' 'It will be quite evident that the constant force spring I32 will be highly advantageous in'that it will result in a uniform feed by the staple feeder I26 in contrast to the commonly used coil spring which 'ext'ertsa decreasing feeding force as the staples areused. i

As shown in Figure 17,-a spring device I40 in accordance with this invention may be used to effect a clamping action s uchas, for example, as a substitute for conventional book ends in clamping together a plurality of books I42. Ihe spring device I40 is formed with a constant set and is coiled at opposite ends to form coils I44 and I46. It will be apparent that, irrespective of the thickness of the books being held and correspondingly irrespective of the distance between coils I44 and I46, the spring device I40 will exert a substantially fixed force against the books.

As shown in Figure 18, a spring device in accordance with this invention is of great utility where it is desired, for example, to, in efiect, go around a corner. Here a spring 2' in accordance with this invention has one end coiled about a bushing I48 which is mounted for rotation on shaft I50 and its other end coiled about a bushing I52 which is freely mounted for rotation on shaft I54. Spring 2 has a constant set which places a natural radius in the spring 2' which is equal to the equal radii of bushings I48 and I52. It will be noted that in passing from bushing I48 to bushing I52, spring 2 passes around a spool I56 which is freely mounted for rotation on a shaft I58.

Since spring 2' has a constant set and bushings wrapped on the side of the spool I55 facing spring from bushing I52. The passage of spring 2' around the corner formed by spool I56 will not disturb this equilibrium since, in passing about spool I56, spring 2' is being-unwrapped on the side of the spool facing bushing I63 anamount exactly euqivalent to the amount it is being unbushing I 52. Thus the forces created by the unwrapwping incident to passing around spool I56 will exactly balance each other. It will be apparent that this ability to change the direction of the operation of spring 2' without disturbing in any way its force characteristics is an extremely useful one. I I v Q .As shown in Figure 19,- where a core is to be utilized, the spring in accordance with thi's invention may take the form of a helix. Here we have a core I60 mounted for rotation in bearings I62. A spring I54 is secured to the one end of the core at I66.

H Spring I 84 is helical in form andis set so that thenatural radius of each segment of the spring is smaller than the radius of the core so that the spring lies flat against the core.- Here again will be apparent that the force exerted by the spring I54 will result from that increment of the s'pring which is being unwrapped from the core and which has not yet been straightened. The set placed in a helical spring device such as described may be varied in accordance with the principles set forth and illustrated above. As shown in Figures 20 and 21, the springs in accordance with this invention may be utilized to produce clips. A circular clip .Il0' which is less than 360 (see Fig.,20) or a similar clip I12 which has overlapping ends can readily. be fashioned by taking a preset spring such as the-spring 2 and cutting Off increments of the desired length which will tend to assume the natural radius set in the spring. Formation of clips in this manner is very advantageous since it eliminates the heretofore used heat treating processes utilized to make clipsas clip I70. The formation of clips having overlapping ends such as the clip I72 has not heretofore been possible by a practicable process.

It will be apparent that the basic uses for spring devices in accordance with this invention are numerous and varied. Exemplary are: ('1) as a spring (extension or compression); (2) as a self-adjusting clamp, clip, or wrapping; (3) as a Vernier force compensator; (4) as a transducer for converting energy from one system to another; (5) as an automatic coiling device; (6') as a friction band; ('7) as a telescopic tube form; and (8) as a means of power or motion transmission.

The flat or receding force characteristic and the great extendability are useful as a spring where constant loads are required. This is wherever levers, pulleys and dead weights are currently used for replacement of, or in conjunction with, torsion, spiral, normal extension, compression, or power springs.

An example of a desirable application for a truly negative gradient is in opening and closing devices. Here it is desirable to start the opening with minimum force but to assure greater restraint in the open position. A spring having a flat force-deflection characteristic makes a highly desirable means of replacing counter weights and sash weights. Many applications 'plifies braking arrangements. accordance with this invention acts as an automatic friction band that exerts uniform pressure around circular drums.

'result from the small cubical space required by a negative spring in its coiled state, and its ability to act around pulleys.

As a transducer for converting mechanical energy to electric modulation or to magnetic "modulation, the negative spring is useful because of the solid nature of the free coil. The device is useful as a variable resistor, the modulation of which is evenly continuous, and not by incremental steps. The coil form also makes it useful 'for changing the amount of laminated core iron in a magnetic field. It can be utilized as a potentiometer slide-wire and for vernier adjustment of "a force member.

Simplifications of mechanisms for the reeling spring as a self-winding tape, which automatically coils itself tightly.

As a friction element, the negative spring sim- A simple clip in It is no longer necessary in designing braking devices to think only of rigid shoes'or flexible bands which are externally pressed on drums or shafts by springs-and lever system. The braking pressure can now be inherent in the brake band member.

1 Because the negative spring offers active pressure of coil on coil, telescopic tube forms may be developed for new functions. It is practical to control such attributes as light-tightness, leakproofness and lateral rigidity in this device.

Finally, to transmit power or motion, designers can consider the spring as: (1) a means of translating linear into circular motion or vice versa, and'(2) as a pulley-belt with a single leg and automatic take-up features. Applications to circuit tuning augur the elimination of take-up springs and flexible bands with their replacement problems.

It will be apparent that the above description and examples are for purposes of illustration only and that it is desired to be limited only as set forth in theclaims.

' What is claimed is:

' 1. A spring device comprising a pair of mandrels, means supporting said mandrels for rotation, a resilient metal strip, the opposite'ends of said strip being' coiled on said mandrels, each increment of said strip being set to naturally of said circles being sufficiently small so that the coiled increments will fit tightly against the surfaces of said "mandrels.

2. A spring device comprising a pair of mandrels having different diameters, a resilient metal strip, the opposite ends of said'strip being coiled around said mandrels, the increments of said strip being set on radii sufliciently small to cause the increments to fit tightly against said mandrels, and the radii of said increments varying progressively from one end of said strip to the other.

3. A spring device comprising a pair of mandrels, a resilient metal strip, the opposite ends of said strip being coiled around said mandrels, each increment of said strip being set to normally assume the shape of a portion of a circle and being set to fit tightly against the surface on which they rest, and means between said mandrels to deflect the portion of the strip between the mandrels to dispose the portions of the strip on opposite sides of said means in angular relation.

4. The spring device set forth in claim 3 in which said mandrels have the same diameter and the normal set of the spring, when unstressed, is uniform throughout its length.

WILLIAM J. COOK.

-References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 122,288 Smith Dec. 26, 1871 377,489 Logan Feb. 7, 1888 1,010,130 Dufiy Nov. 28, 1911 1,331,677 Schachter Feb. 24, 1920 1,860,878 Webb et al. May 31, 1932 1,977,546 Fornelius Oct. 16, 1934 2,175,516 Bugatti Oct. 10, 1939 2,192,101 Peskin Feb. 27, 1940 2,363,113 Bennet Nov. 21, 1944 2,457,705 Moran Dec. 28, 1948 FOREIGN PATENTS Number Country Date 94,867 Switzerland May 16, 1922 442,681 Great Britain Feb. 13, 1936 609,673 Great Britain Oct. 5, 1948 

